Form Submit Question : Using Thick Proxy But They Can Still See My Computer

I am submitting names to form, (not cpa or anything). Everytime I enter a new name I change my IP so that it appears to be coming from somewhere else. However, if I submit around 10 names to fast I will get

"To many submissions from same computer"

The form is not recognizing me and allows me to keep submitting, but I want to know how they know it is the same computer even if I am clearing my cookies and changing my proxy after every single submission

I disable javascript and if I start submitting to fast it will still say "we are getting to many subscribes from this computer" I am using Hide my IP premium proxies Does hide my ip not use level 1 proxies. How is it still telling what computer it is coming from

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